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I have 50 crepe myrtles - this is their third year - all of the leaves are turning black - the bark is still green so I know they are not dead - I have sprayed for fungus, insects, fertilized and nothing seems to be helping. My inclination is to prune them back and give up for this year. Please give me some advice.
My guess is that you had aphids on them, they secrete honeydew which can then lead to sooty mold forming on the leaves. If that's what it is, I wouldn't prune it (unless you were planning to anyway for shape, etc), the leaves will fall off this winter and when they grow back next year. The trick is to get rid of the aphids early next year before the sooty mold can form--I'm guessing this year you didn't spray until you saw the black stuff?
OK - my crepe myrtles are the same... so I'm off to buy something to help kill the infestation of aphids I can clearly see under each leaf... but is there any way to kill the black fungus which has grown on the leaves, or do I have to wait for next year to see my myrtles return in all their glory?
The black stuff is hard to remove, fungicides will kill it but the problem is the dead fungus is still black and ugly, so you have to wash off the leaves to get rid of it and it's not as simple as just rinsing with the hose, you have to work at it a bit. I've had luck getting rid of it on young small plants that didn't have it very badly, but if this is a large tree you're probably better off waiting for the leaves to fall off in the fall. Then next year make sure you keep an eye out regularly for the aphids and catch them before they coat the whole tree in honeydew.
